This invention relates to a radiation-sensitive positive resist adapted for the formation of a fine pattern used in the manufacture of, for example, an integrated semiconductor device and photomask.
Hitherto, the process of forming a fine pattern for the manufacture of an integrated semiconductor device or photomask has practically been based on the application of a photoresist sensitive to visible rays or ultraviolet rays. In recent years, the technique of utilizing radiation such as electron beams, X-rays and deep ultraviolet rays has been developed to form a fine pattern for the manufacture of, for example, a semiconductor device due to demands for its high integration. As a result, various radiation-sensitive resists have been proposed. The typical radiation sensitive positive resist has been prepared from a compound belonging to a poly (alkyl methacrylate) series represented by poly(methyl methacrylate) (PMMA), or a poly(olefin-sulfone) series represented by poly(butene-1-sulfone) (PBS). However, any of the compounds hitherto used as a positive resist has been found defective in the fundamental respects and failed to be put to practical application.
For example, the above-mentioned PBS has the drawbacks that it has a far lower resolution than polymethyl methacrylate, though having a radiation sensitivity ten times or more higher than said PMMA; has poor adhesion to a semiconductor substrate or mask substrate; is liable to be thermally decomposed, and consequently is little adapted for the application of dry etching indispensable for fabrication of high density device structures.
On the other hand, PMMA, in spite of its high resolution, also has the drawbacks that it has a low radiation sensitivity. When it is employed at relatively low radiation dosages, its high resolution has to be sacrificed. Consequently, it is unadapted for the practical quantity production of a semiconductor device, or photomask, particularly, a highly integrated circuit. Further, in order to improve the sensitivity of PMMA, attempts are made to employ high molecular weight PMMA. However, such high molecular weight PMMA can not be uniformly spin coated on a semiconductor substrate, and noticeably swells during development, leading to a decline in the precision with which the resist is patterned. Consequently, these attempts give rise to serious defeciencies in processability or resolution of PMMA. Studies have been made to develop other of poly (alkyl methacrylate) series having a higher radiation sensitivity than PMMA. However, various forms of poly (alkyl methacrylate) proposed to date are disadvantageous in that they are all inferior to PMMA in respect of resolution, and, when heated, bring about the deformation of the resultant resist pattern.
Hitherto, attempts have also been made to introduce a halogen element having a high radiation sensitivity into one of the side chains of an acrylate polymer to provide a positive resist highly sensitive to radiation. For example, there have been reported poly(methyl .alpha.-chloroacrylate) in which chlorine is substituted with the .alpha.-hydrogen of polymethyl acrylate, and poly(fluoro alkyl methacrylate) in which fluorine is substituted into the ester side chain. However, the poly(fluoroalkyl methacrylate) has the drawbacks that it has unsatisfactory heat resistance due to its low glass transition temperature, and poor adhesion to a semiconductor substrate, and is inferior to PMMA in respect of workability and resolution. On the other hand, although poly(methyl .alpha.-chloroacrylate) has a high glass transition temperature and good heat resistance, its sensitivity is only slightly increased compared with PMMA, and yet it is inferior to PMMA in respect of resolution.